The ultimate aim of this study is to elucidate the role relaxin plays in parturition in humans. To this end we are trying first to determine the total potential of the relaxin molecule in a variety of species. Such seemingly unrelated activities as muscular relaxation of a uterus muscle and the widening of the symphysis pubis as well as the loosening of the sacroiliac joints will be investigated in relation to the chemical structure of the hormone. Through a series of structure-function studies we hope to be able to find centers on the surface molecule that are particularly important for one or the other function and thus to learn something about the molecular mechanism of action. In addition, studies of relaxin from ancient species (such as shark) will continue in order to shed light on the process of biological evolution of the hormone receptor repair.